L-cystine is the L-enantiomer of the sulfur-containing amino acid cystine. It has a role as an EC 1.2.1.11 (aspartate-semialdehyde dehydrogenase) inhibitor, a flour treatment agent, a mouse metabolite, a Saccharomyces cerevisiae metabolite and a human metabolite. It is a cystine, a non-proteinogenic L-alpha-amino acid and a L-cysteine derivative. It is a conjugate acid of a L-cystine anion. It is an enantiomer of a D-cystine. It is a tautomer of a L-cystine zwitterion. L-Cystine can improve hyperlipidemia by restoring LPL and HSL activities.L-Cystine protects against the toxicity of PQ by maintaining reduced glutathione levels in the cells. Co-administration of l-cystine and l-theanine before vaccination may enhance the immune response to influenza vaccine in elderly subjects with low serum total protein or hemoglobin.

Albaspidin AA displays strong antibacterial activity against the vegetative form of P. larvae (MIC ranging from 0.168-220 uM). It may have in vitro nematocidal activity against L4 stage larvae.